In the last decade, the Internet paradigm has been evolving toward a new frontier with the emergence of ubiquitous and pervasive systems, including wireless sensor networks, ad hoc networks, RFID systems, and wireless embedded systems. In fact, while the initial purpose of the Internet was to interconnect computers to share digital data at large scale, the current tendency is to enable ubiquitous and pervasive computing to control everything anytime and at a large scale. This new paradigm has given rise to a new generation of networked systems, commonly known as Internet-of-Things or Cyber-Physical Systems. The research community has actively investigated the underlying challenges pertaining to these systems, as they fundamentally differ from the classical problems due to their inherent constraints. This special issue presents six papers covering various topics in personal and ubiquitous computing. The first paper entitled ‘‘RiSeG: A Ring Based Secure Group Communication Protocol for Wireless Sensor Networks’’ deals with security in ubiquitous systems. The paper presents a new approach for secure group management in wireless sensor networks. The proposed approach is based on a logical ring architecture, which permits to alleviate the group controller’s task in updating the group key. The proposed scheme also provides backward and forward secrecy, addresses the node compromise attack, and gives a solution to detect and eliminate the compromised nodes. The authors evaluated their scheme in terms of storage, computation, and communication costs and compared its behavior against the Logical Key Hierarchy (LKH) scheme. It has been shown that RiSeG requires less storage cost and reduces computation and communication costs at the Group Controller as compared with LKH. The paper goes beyond theoretical work and proposes a realworld implementation, which first proved that RiSeG is applicable to WSNs and also showed that the performance results in terms of execution time, energy consumption, and memory consumption are satisfactory. The second paper entitled ‘‘Stability routing with constrained path length for improved routability in dynamic MANETs’’ addresses the problem of enhancing the routing validity in mobile wireless multi hop ad hoc networks. In proactive routing, routes are established and updated periodically and consequently loose their pertinence as time tics away from the start of their updating instants. Authors argue that routability, defined as the validity of established routes, stands among the most centric metric impacting the network efficiency. Indeed, in dynamic networks, traffic routed through invalid routes not only amounts to a waste of valuable resources but will never be delivered to its destination. In the quest of improving routability in dynamic networks, the authors considered a two-constrained QoS routing problem with one superlative constraint and one comparative constraint. In its general form, this is an NP hard problem. The authors proposed a novel exact algorithm and then instantiated the problem to solve the optimal integer weight-constrained path length A. Belghith (&) University of Manouba, Manouba, Tunisia e-mail: abdelfattah.belghith@ensi.rnu.tn
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